'Doesn't feel right': NFL world erupts over Tom Brady announcement

Six-time Super Bowl champion quarterback Tom Brady says he is leaving the New England Patriots after 20 years with the team, stunning fans of the NFL franchise and adding a dramatic twist to the league's off-season.

With free agency beginning on Wednesday, the 42-year-old quarterback left no doubt in a social media postthat he would not return to New England.

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During his celebrated tenure he set many NFL records, including most victories and appearances in the Super Bowl and most playoff wins. He won a record four Super Bowl Most Valuable Player trophies.

"Although my football journey will take place elsewhere, I appreciate everything that we have achieved and am grateful for our incredible TEAM accomplishments," Brady wrote in a Twitter post on Tuesday that instantly went viral.

He did not elaborate on his plans or next steps in his career. Previously, he has said he wanted to continue playing and was unlikely to retire.

"I had hoped this day would never come, but rather that Tom would end his remarkable career in a Patriots uniform after yet another Super Bowl championship," team owner Robert Kraft said in a written statement.

"Unfortunately, the two sides were unable to reach an agreement to allow that dream to become a reality."

World reacts to shock Tom Brady announcement

Patriots head coach Bill Belichick, who formed one of the NFL's most enduring and successful partnerships with Brady, said in a written statement that the quarterback was one of the Patriots program's "original creators."

“Sometimes in life, it takes some time to pass before truly appreciating something or someone but that has not been the case with Tom,” said Belichick.

“He is a special person and the greatest quarterback of all-time.”

Belichick selected out of Michigan Brady in 2000 with the 199th pick of the NFL draft. Brady spent his first season as a backup, then stepped in for the injured Drew Bledsoe in 2001 as starting quarterback. He led the team to their first ever Super Bowl victory at the end of the 2001-2002 season.

Brady also had detractors who accused him of cheating in 2015 by ordering Patriots employees to improperly lower the pressure of footballs before an NFL playoff game.

Brady was ultimately suspended four games for the incident that became known as "deflategate" even though he denied wrongdoing.

Speculation over where he may land next has been rampant for months, as the Patriots' most recent season ended in a humiliating at-home defeat against the Miami Dolphins, followed up by a shock loss to the Tennessee Titans in the playoffs.

Suitors have reportedly included the Los Angeles Chargers and the Tampa Bay Buccaneers, the latter an early betting favourite.